Wear-resistant surface composite materials and method for producing same

ABSTRACT

Materials, such as metals, alloys and other products are provided with improved wear-resistant surfaces comprised of a hard monocarbide phase in the form of filaments within the material matrix.

United States Patent Kotval et al.

[ 1 Dec. 30, 1975 WEAR-RESISTANT SURFACE COMPOSITE MATERIALS AND METHODFOR PRODUCING SAME Inventors: Peshotan S. Kotval, Hartsdale; HenriHatwell, White Plains; Frank P. Gortsema, Croton, all of NY.

Assignee: Union Carbide Corporation, New

York, NY,

Filed: May 4, 1973 Appl. No.: 357,080

Related US. Application Data Continuation-in-part of Ser. No. 270,241,July 10, 1972, abandoned US. Cl 29/195; 161/88 Int. Cl. B32B 15/04 Fieldof Search 29/195 A; 161/88, 89, 94,

Primary ExaminerL. Dewayne Rutledge Assistant ExaminerE. L. WeiseAttorney, Agent, or FirmWilliam R. Moran [57] ABSTRACT Materials, suchas metals, alloys and other products are provided with improvedwear-resistant surfaces comprised of a hard monocarbide phase in theform of filaments within the material matrix.

11 Claims, N0 Drawings This application is a continuation-in-part ofU.S. application Ser. No. 270,241 entitled Improved Wear- ResistantSurface Composite Materials and Method for Producing Same filed July 10,1972, by P. S. Kotval, H. Hatwell and F. P. Gortsema, now abandoned.

This invention relates to improved wear resistant surface compositematerials and to a method for their production. In one aspect theinvention relates to metals, particularly aluminum alloys with anespecially wear-resistant duplex surface comprising a large areafraction of hard refractory metal monocarbide phases. In a furtheraspect, the invention relates to the use of refractory metal monocarbidephases in the form of fibers, felts, tapes and woven fabrics and amethod for composi'ting these materials in the surface of otherwisewear-prone materials such as aluminum alloys, to impart exceptionallyhigh wear-resistance to the composite surface.

As is well known, many materials such as metals, alloys and otherproducts exhibit poor wear properties and as a consequence, the use ofsuch materials is se- 'verely restricted in applications wherewear-resistance is an important requirement. In the prior art, attemptsat improving the poor wear-resistance of materials, such as aluminum andits alloys, have been focused on two principal methods: (a) the use ofanodizing treatments which permit the formation of a hrad oxide film onthe surface of aluminum, and (b) the use of surface coating treatments,such as plasma-spraying, flameplating and similar methods which involvethe deposition of a wear-resistance phase or phases on the surface ofaluminum alloys. These state-of-the-art methods go some way towardfulfilling the requirements of improved wear-resistance for aluminumalloys. However, both methods suffer from limitations. The films createdby anodizing treatments are mechanically weak and the enchancement ofwear-resistance is not maintained once rupture of the film occurs.Further, there is a physical limitation of the thickness of the filmswhich can be created on aluminum alloys. The methods involving thedeposition of various hard phases to improve wear behaviour suffer fromthe disadvantage that they are not readily adaptable to cases wheremechanical precision is necessary in the finished part and also have thedisadvantage of a propensity (under certain conditions) towardseparation of the wear-resistant coating from the substrate.

In marked contrast to both types of the above-mentioned prior artmethods of improving wear resistance, the present invention teaches thatthe entire surface of the alloy need not be covered by thewear-improving phases. Instead, the utilization of the hard refractorymono-carbide phases, for example in the form of a woven tape permits thefinal surface to have a composite surface structure wherein up to 80percent of the surface area is comprised of regions of the hardmononcarbide phase embedded within the matrix of the alloy. the fibrousnature of the wear-improving phase permits a continuous presence of thehard phase even in conditions of abrasive wear. Thus, the presentinvention represents a marked improvement over the prior art methods(e.g., plasma-sprayed powders) where a parti- 2 cle of hard phase, onceremoved during abrasive wear ceases to provide any wear-improving role.

Accordingly, one or more of the following object: will be achieved bythe practice of this invention. It i: an object of this invention toprovide improved wea resistant surface composite materials and to amethor for their production. A further object of the inventior is toprovide materials with a duplex composite surfact which exhibitexceptionally improved wear resistanct in comparison to the untreatedmaterial surface. An other object of the invention is to employrefractory metal carbides in the form of filaments to provide a duplexcomposite surface having improved wear-resist ance. A still furtherobject of this invention is to pro vide aluminum alloys with improvedwear-resistance surfaces. Another object is to provide non-metallicmaterials such as epoxy and phenolic resins which have improvedwear-resistant surfaces. These and other objects will readily becomeapparent to those skilled ir the art in the light of the teachingsherein disclosed.

In its broad aspect this invention relates to improvec wear-resistantcomposite materials and to a process f0] their preparation. Thecomposites are characterized by a surface which has a duplex compositestructure comprised of (a) a matrix material of poor wear resistance and(b) not less than about 50 percent area fractior and up to about percentarea fraction of a hard fibrous monocarbide phase. The monocarbide phaseis represented by the general formula MC wherein M is 2 metal from thegroup tantalum, titanium or tungsten and C is carbon and is in the formof filaments of between about 2 and about 15 microns in diameter beingpresent at the composite surface as sections of varying orientations,the remainder of the surface being comprised of matrix material.

By the term filaments as employed throughout the specification andappended claims is meant wover fabrics, tapes, felts, chopped fibers,and the like composed of the metallic monocarbides. These metallicmonocarbides are prepared by the process disclosed ir U.S. Pat. No.3,403,008.

It has been observed that a wide variety of materials which are normallycharacterized by poor wear-resistance, can have their wear-resistancemarkedly improved by the teachings of the instant invention.Illustrative materials include, among others, aluminum silver, copper,and their alloys, non-metallic matrices such as epoxy and phenolicresins, and the like. F01 example, aluminum alloys which normallyexhibit pooi wear-resistant properties include those based on thealuminum-silicon alloy system particularly hyper eutectic combinationswhich are commonly used a: casting grade aluminum alloys. Also includedare silver and silver containing alloys such as those used for braz ingapplications, copper and its alloys as well as othe matrices. Aspreviously indicated the invention is alsr applicable to othernon-metallic matrices such as epox resins and phenolic resins.

The ability to produce the materials of this inventioi withexceptionally enhanced wear-resistance result from the discovery thatwhen filaments of the monocar bides of the aforementioned refractorymetals are i1 contact with materials such as aluminum and its alloy inthe molten state, the filaments are rapidly wetted by the molten metal.A feature of this wetting reactioi is the formation of intermetallicphases at the interface between the individual fibers and filaments ofth monocarbide phase and the adjacent metallic matrix In practice, thematerial of this invention can be onveniently prepared by a variety ofmethods. For xample, the ready wettability of the textile form of theefractory metal monocarbides by materials such as luminum and its alloyslends itself to a method of mbedding the wear-resistance-impartingmonocarbide ito the material directly during the casting operation. orexample, the mold can be lined with the monocar ide filaments and thenormal casting operation carried ut. As previously indicated thefilaments can be em loyed in a variety of forms. The particularconfiguraion of the mold may, in part, determine the preferred arm ofthe filaments.

In many instances, it has been observed that filaients in the form oftapes are convenient for lining the tterior surfaces of the mold. Thethickness of the tape a not necessarily critical as long as sufficientmetallic monocarbide filaments are present to improve the suracewear-resistant properties. In practice it has been bserved that markedimprovements are obtained hen the surface composite structure iscomprised of ot less than about percent area fraction and up to bout 90percent area fraction of the hard fibrous ionocarbide phase.

As previously indicated the present invention can rovide mechanicallyprecise castings which have im- 35 roved wear-resistance. Inasmuch asthe metallic ionocarbides are placed in the mold prior to the marixmaterial, the overall configuration of the cast artile has the samedimensions as the cast article without EXAMPLE I A tape of satin-weavewoven fabric comprised of tantalum carbide prepared by the processdisclosed in US. Pat. No. 3,403,008 was used to create a compositesurface on 6061 aluminum alloy. The filaments comprising the tape were5,11. in diameter.

The apparent molecular weight of the tantalum carbide was 191.4, showingthat the material of the woven fabric approximated closely idealstoichiometric TaC (molecular weight 192.96). A tape, 0.5 inches wide by3.0 inches long, was placed in an alumina crucible and a bar of 6061aluminum alloy was placed over the tape. The crucible and contents wereheld in an argon atmosphere furnace at 700C for 5 minutes. Upon cooling,the as-cast 6061 alloy was found to have the said tape embedded fullywithin the lower surface of the ingot resulting in a composite surface.Using part of the above sample and utilizing the technique of thin foiltransmission electron microscopy, electron diffraction patterns wereobtained from the region of the interface between the TaC filaments andthe 6061 alloy matrix. The patterns revealed that in addition to theface-centered-cubic 6061 matrix and the face-centerd-cubic 6061 matrixand the face-centered-cubic TaC fibers, there was a tetragonal Al Taintermetallic phase formed at the fiber/matrix interface, thus providingevidence of good bond formation.

Blocks /4 inch wide X inch long X inch deep were cut from the sample of6061 alloy with the composite matrix plus TaC fiber surface. Thecomposite surface was tested for wear-resistance under varying loads ina standard Alpha model wear-testing machine. In this test the testsurface is subject to wear against a 4620 steel ring hardened to ahardness of R 58 to 63. The relative wear parameter of test material isgiven by measuring the volume of the scar created on the surface by weartest. The results obtained are set forth in Table I below:

measure 1e monocarbides.

The filaments employed in this invention are also seful for impartingimproved wear-resistance to artiles prepared by hot pressing powderedmatrix materi- Is. For example a tape, felt, woven fabric, or choppedbers of the metallic monocarbide can be placed on ne or more surfaces ofa die, powdered matrix mateal added, and the composite hot pressed toform the esired article. 60

The present invention thus provides a simple and onvenient technique forimparting improved wear- :sistance to surfaces of a variety ofmaterials. Without ny complicated processing steps, other than those|volved in normal material fabrication, a wear-resistnt composite duplexsurface for the material can be irectly created.

The following examples are illustrative:

The wear scar volumes of the composite surface of the present inventionare compared in Table I with the values for wear scar volumes for atypical aluminum alloy. It is evident that the composite surface of thepresent invention has wear characteristics which represent athousand-fold improvement over the wear characteristics of conventionalaluminum alloy surfaces.

EXAMPLE [1 A tape of satin weave woven fabric comprising essentially oftantalum carbide was positioned into the bottom of a mold into which aBuehler No. 20-8133-001 Epoxy Resin was cast. Upon curing the resultantEpoxy block was found to have one surface with a duplex compositemicrostructure comprising area% TaC in Epoxy matrix. Blocks 8'4 inchwide, inch long and 4/8 inch deep were cut from these Expoxy blocks withmatrix plus TaC fiber surface. The composite surface was tested forwear-resistance under varying loads in a standard Dow-Corning Alphamodel Wear-testing Machine. ln this test the test surface is subjectedto wear against a 4620 steel ring hardened to a R 58 to As is evidentfrom Table III, a Surface Composite comprising 75 area percent of TaCphase within a 6061 alloy matrix represents an improvement of up to athousand-fold in the measured values of wear scar vol- 63. The relativewear parameters for the composite 5 ume compared to the bare 6061 alloy.Compared to the surface of an Epoxy Matrix, with varying area fractionswear-resistance of even the hypereutectic Al-l8 weight of the fibrousTaC phase is compared with parameter percent Si alloy, the wearproperties of Surface Comfor the bare Epoxy block in Table 11. positematerials represent an increase of between 10 and 30-fold. 10 In themeasurement of wear behavior it is necessary Matenal Lubrlcam wear Scarvolume to take into account the total system wear; i.e., the Epoxy withPress Fluid 30 lbs. 105 x 10- cm wear measured on the test block as wellas the wear Z'fgggmeasured on the mating rotating member. Bearing Epoxywith press Fluid 30 162 X 0-6 this in mind, it is significant to comparestateof-the-art 60 wear-resistant materials with the Surface CompositeTaC tape v Epoxy press Fluid 30 I798 X 10-6 a materials of thisinvention. In Table 111 are included two (untreated) suchstate-of-the-art bulk composite materials produced via conventionalpowder metallurgy techniques: Ferro-TiC developed by ChromalloyCorporation EXAMPLE m and the Al graphite composite developed by ToyoKogyo Co. as a wear-resistant rotor apex seal for the Comparisons weremade between the wear resistance Mazda automobiles rotary-piston engine.The Ferof the surface composite materials of this invention and ro-TiCmaterial provides good wear-resistance but iS known materials usingstandard wear tests. very abrasive vis-a-vis the wear of the matingring. Ring The wear data was obtained using a LFW-l model weight lossvalues for tests with Ferro-TiC are a factor Wear-Testing Machinemanufactured by the DO C0 of two higher than the comparable values fortests with ning Corporation. As described in ASTM Standard SurfaceComposite materials in 6061 and 2024 alloy Test Method D 2714-68, alltests were carried out on matrices. The A1 graphite composite materialshows stationary re tangular inch d X 5 8 inch 1 g X higher values forboth Ring Weight Loss and Wear Scar inch deep) test blocks pressed, witha pre-determined Volume when compared to the Surface Composite load,against a rotating ring. The wear properties mea- Materials thus clearlyindicating the superior wear besured were: (i) Volume of Wear Scar onthe test surhavior of the materials of this invention. face of wearblock material; (ii) Weight change of the It should be noted that inaddition to the wear propmating ring; and (iii) the friction forcemeasured at erties of the Surface Composite materials beingsupeintervals during the test. The wear data listed in Table rior to thestate-of-the-art materials, the fabrication of 111 were obtained underthe following conditions of Surface Composite materials does not requireany testing: major modification of either the technology or theeconomics of conventional practice for casting alumi- Mating Ring: 4620-Steel; R,.=58-62; Surface num y inches In contrast, the state-of-the-artwear-resistant com- Lubricant: Mobil 5606-A fluid Load, 30 posrtesmentioned hereinbefore, are fabricated by rela- Wear Speed: 180 r.p.m.(Ring diamete 1-3 tively more expensive processing involving sintering,Total revs: 5400 revs.

hot pressing and the like.

Table III Material Tested Wear Scar Ring Weight Coefficient Volume Lossof Friction (XIO' cm) (mg) (at 5400 revs.)

1. Surface Composite 6 to 40 .16 .7 .12 .15

( area percent TaC satin Weave Textile in 6061 aluminum alloy matrix).

2. Surface Composite 32 .15 .11

(75 area percent TiC bias woven tape in 6061 aluminum alloy matrix).

3. Surface Composite 8 to 30 .12 .25 .12 .15

(75 percent TaC Satin Weave Textile in a 2024 alloy matrix).

4. Surface Composite (75 4 .9 .12

area percent TaC Satin Weave textile in a C0- Cr-Ni alloy matrix). 5.Surface Composite 9.5 .81 .11 .12

(75 area percent TaC Satin Weave textile in A1-18w/o Table Ill-continuedMaterial Tested Wear Scar Ring Weight Coefficient Volume Loss ofFriction Si alloy matrix).

6. 6061 aluminum alloy 5998 weight gain .066

7. Al-l8w/o Si alloy 380 .46 .l2

8. Al graphite 124- 13] .65-l.01 .133

composite (Toyo Kogyo) 9. Ferro TiC (Chromalloy) 2-7 L28 .133

Although the invention has been illustrated by the preceding examples itis not to be construed as being limited to the materials employedtherein, but rather the invention encompasses the generic area ashereinbefore disclosed. Various modifications and embodiments of thisinvention can be made without departing from the spirit and scopethereof.

We claim:

1. An improved wear-resistant surface composite material, the surface ofwhich has a duplex composite structure comprised of (a) a matrixmaterial of poor wear-resistance and (b) not less than about 50 percentarea fraction and up to about 90 percent area fraction of a hard fibrousmonocarbide phase, said monocarbide phase being represented by thegeneral formula MC wherein M is a metal selected from the groupconsisting of tantalum, titanium or tungsten and C is carbon, saidmonocarbide phase being in the form of filaments between 2 and about 15microns in diameter and being present at the composite surface assections of varying orientations, the remainder of the surface beingcomprised of the matrix of the said material.

woven fabric is present 2. The composite of claim 1 wherein said matrixmaterial is aluminum.

3. The composite material of claim 1 wherein said matrix material is analuminum alloy.

4. The composite material of claim 1 wherein said matrix material is acasting grade aluminum-silicon hypereutectic alloy composition.

5. The composite material of claim 1 wherein M of said general formulais tantalum.

6. The composite material of claim 1 wherein M of said general formulais titanium.

7. The composite material of claim 1 wherein M of said general formulais tungsten.

8. The composite material of claim 1 wherein said filaments are presentas a woven fabric.

9. The composite material of claim 1 wherein said filaments are presentas a felt.

10. The composite material of claim 1 wherein said filaments are presentas chopped fibers.

11. The composite material of claim 9 wherein said as a tape.

1. AN IMPROVED WEAR-RESISTANT SURFACE COMPOSITE MATERIAL, THE SURFACE OFWHICH HAS A DUPLEX COMPOSITE STRUCTURE COMPRISED OF (A) A MATRIXMATERIAL OF POOR WEAR-RESISTANCE AND (B) NOT LESS THAN ABOUT 50 PERCENTAREA FRACTION AND UP TO ABOUT 90 PERCENT AREA FRACTION OF A HARD FIBROUSMONOCARBIDE PHASE. SAID MONOCARBIDE PHASE BEING REPRESENTED BY THEGENERAL FORMULA MC WHEREIN M IS A METAL SELECTED FROM THE GROUPCONSISTING OF TANTALUM, TITANIUM OR TUNGSTEN AND C IS CARBON, SAIDMONOCARBIDE PHASE BEING IN THE FORM OF FILAMENTS BETWEEN 2 AND ABOUT 15MICRONS IN DIAMETER AND BEING PRESENT AT THE COMPOSITE SURFACE ASSECTIONS OF VARYING ORIENTATIONS, THE REMAINDER OF THE SURFACE BEINGCOMPOSED OF THE MATRIX OF THE SAID MATERIAL.
 2. The composite of claim 1wherein said matrix material is aluminum.
 3. The composite material ofclaim 1 wherein said matrix material is an aluminum alloy.
 4. Thecomposite material of claim 1 wherein said matrix material is a castinggrade aluminum-silicon hypereutectic alloy composition.
 5. The compositematerial of claim 1 wherein M of said general formula is tantalum. 6.The composite material of claim 1 wherein M of said general formula istitanium.
 7. The composite material of claim 1 wherein M of said generalformula is tungsten.
 8. The composite material of claim 1 wherein saidfilaments are present as a woven fabric.
 9. The composite material ofclaim 1 wherein said filaments are present as a felt.
 10. The compositematerial of claim 1 wherein said filaments are present as choppedfibers.
 11. The composite material of claim 9 wherein said woven fabricis present as a tape.